Method and apparatus for improving heat stability in temperature-sensitive geotechnical applications

ABSTRACT

A geotechnical application including a geotechnical site having a process area sensitive to temperature. A geosynthetic sheet covers the site process area, wherein the geosynthetic sheet includes an ultraviolet (UV) light stabilizer, is substantially impervious to water, and is at least translucent to light. The geosynthetic sheet prevents heat loss to the air which helps to elevate and/or maintain the temperature of the process area.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a non-provisional patent application claiming priority to U.S.Provisional Application Ser. No. 61/831,466, filed Jun. 5, 2013,entitled “Method and Apparatus for Improving Heat Stability inTemperature-Sensitive Geotechnical Applications”, which is herebyincorporated by reference in its entirety.

FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable.

MICROFICHE/COPYRIGHT REFERENCE

Not Applicable.

FIELD OF THE INVENTION

The present invention relates to temperature-sensitive geotechnicalapplications, and more particularly to a method and apparatus forimproving the thermal stability in such applications.

BACKGROUND OF THE INVENTION

Efficient geotechnical applications are, of course, important not onlyto a particular business purpose of an application, but also to theenvironment. Whatever efficiencies can be provided in such applicationsare thus important on many levels, and can have worldwide implications.Many such geotechnical applications are temperature-sensitive.

In some instances, temperatures in geotechnical applications are theresult of an external process, such as with ponds used to store warmprocessing water. In such geotechnical systems, the solution willreadily cool when exposed to the atmosphere due to heat transfer to theair. Further, evaporation during hot and/or dry months may also causecooling. Still further, such evaporation may also cause undesirablefluctuations in the concentration of any added materials in theprocessing water, as may rain during wet periods. Of course, during coolmonths, the external process may require more energy to providesufficiently heated processing water, and may even require that theprocess be halted if sufficiently warm processing water cannot beprovided due to the ambient air temperature.

In other geotechnical applications, desired temperatures result from aninternal process, such as a chemical or biological reaction. Forexample, in precious metal mining involving heap leaching, orecontaining precious metal is piled on top of geosynthetic materials andthen reactive chemicals are trickled through the ore in order to extractthe metals. The solution then travels to the bottom of the ore pilewhere it is harvested. As the reaction proceeds in such applications(which can take months through recirculation of the solution), heat isproduced which advantageously raises the temperature of the heap (sincethe rate of the reaction will typically increase with temperature, theproduced heat thereby increases the overall yield of the heap). However,because the heap is exposed to the atmosphere, some of the generatedheat is undesirably dissipated due to heat transfer to the air. Also,especially during hot and/or dry months, evaporation of the leachingsolution into the atmosphere will occur, thereby causing undesirablefluctuations in concentration of the leaching solution. Further, duringwet periods, the leaching solution may be diluted by rain water (therebydecreasing the effectiveness of any concentration-driven reactions) andduring cool months, the leaching process may even be required to behalted at times because an effective heap temperature cannot bemaintained due to the ambient air temperature.

The present invention is directed to overcoming one or more of theproblems set forth above.

SUMMARY OF THE INVENTION

In one aspect of the present invention, a geotechnical application isprovided including a geotechnical site having a process area sensitiveto temperature, and a geosynthetic sheet covering the site process area.The geosynthetic sheet includes an ultraviolet (UV) light stabilizer, issubstantially impervious to water, and is at least translucent to light.

In one form of this aspect of the present invention, the sheet is linearlow density polyethylene (LLDPE). In other forms, as well as LLDPE, thesheet may be one or more of high density polyethylene (HDPE),polypropylene (PP), ethylene propylene diene monomer (EPDM),thermoplastic olefins (TPO), ethylene vinyl acetate (EVA) and/or otherthermoplastic materials and their coextruded variations.

In another form of the present invention, the sheet is sufficientlytranslucent to allow visual inspection of underlying materials in theprocess site through the sheet, and in a further form the sheet issubstantially transparent.

In still another form of the present invention, the UV light stabilizerincludes a hindered amine light stabilizer (HALS) formulated to resistextraction/destruction by chemicals used in the geotechnical siteprocess area. Thermal stabilizers are also included to stabilize thegeomernbrane under elevated temperatures in addition to providingextended longevity due to the syngergistic effect between the UVstabilizer and the thermal stabilizer. The thermal stabilizers alsoresist extraction/destruction by chemicals and do not add color/opacityto the geomembrane.

In another aspect of the present invention, a geosynthetic sheet isprovided for covering a geotechnical site having a process areasensitive to temperature. The geosynthetic sheet includes an ultraviolet(UV) light stabilizer, is substantially impervious to water, and is atleast translucent to light.

In one form of this aspect of the present invention, the sheet is linearlow density polyethylene (LLDPE). In other forms, as well as LLDPE, thesheet may be one or more of high density polyethylene (HDPE),polypropylene (PP), ethylene propylene diene monomer (EPDM),thermoplastic olefins (TPG), ethylene vinyl acetate (EVA) and/or otherthermoplastic materials and their coextruded variations.

In another form of the present invention, the sheet is sufficientlytranslucent to allow visual inspection of underlying materials in theprocess site through the sheet, and in a further form the sheet issubstantially transparent.

In still another form of the present invention, the UV light stabilizerincludes a hindered amine light stabilizer (HALS) formulated to resistextraction/destruction by chemicals used in the geotechnical siteprocess area.

Other objects, features, and advantages of the invention will becomeapparent from a review of the entire specification, including theappended claims and drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In accordance with the present invention, a geosynthetic sheet may beused as a cover for temperature sensitive geotechnical applications, andmore specifically as a cover for areas in which a process sensitive totemperatures is desired (such as leaching of precious metal ores).

In one advantageous configuration, the geosynthetic sheet or geomembraneaccording to the present invention may be generally formed, with certaindifferences as disclosed herein, of linear low density polyethylene(LLDPE) materials such as heretofore used for geosynthetic products,such as UltraFlex@ textured and smooth geomembranes from GSEEnvironmental, LLC of Houston, Tex.

The heretofore used GSE UltraFlex® textured geomembrane is a co-extrudedtextured linear low density polyethylene (LLDPE) geomembrane accordingto the specifications of Table 1, which meet GRI GM17.

TABLE 1 Minimum Average Value Tested Property Test Method Frequency 1.00mm 1.50 mm 2.00 mm 2.50 mm Thickness, mm ASTM D 5994 every roll 1.001.50 2.00 2.50 Lowest individual reading 0.90 1.35 1.8 2.25 Density,g/cm³, (max.) ASTM D 1505 90,000 kg 0.939 0.939 0.939 0.939 TensileProperties (each direction) ASTM D 6693, Type IV  9,000 kg 11 16 21 26Strength at Break, N/mm Dumbbell, 50 mm/min 250 250 250 250 Elongationat Break, % G.L. 50 mm Tear Resistance, N ASTM D 1004 20,000 kg 100 150200 250 Puncture Resistance, N ASTM D 4833 20,000 kg 200 300 400 500Carbon Black Content, % ASTM D 1603/4218  9,000 kg 2.0-3.0 2.0-3.02.0-3.0 2.0-3.0 (Range) Carbon Black Dispersion ASTM D 5596 20,000 kgNote⁽¹⁾ Note⁽¹⁾ Note⁽¹⁾ Note⁽¹⁾ Asperity Height, mm ASTM D 7466 secondroll .045 .45 0.45 0.45 Oxidative Induction Time, min A5TM D 3895,90,000 kg >100 >100 >100 >100 200° C.; O₂, 1 atm TYPICAL ROLL DIMENSIONSRoll Length, m Double-Sided Textured 213 158 122 100 Single-SidedTextured 236 164 124 100 Roll Width, m 6.86 6.86 6.86 6.86 Roll Area, m²Double-Sided Textured 1,463 1,087 836 690 Single-Sided Textured 1,6191,125 851 690 Note⁽¹⁾ - Dispersion only applies to near sphericalagglomerates. 9 of 10 views shall be Category 1 or 2. No more than 1view from Category 3.

The above described GSE UltraFlex® textured geomembrane has beenavailable with texture on one or both sides, and has been used inapplications that require increased frictional resistance, flexibilityand elongation properties where differential or localized subgradesettlements may occur such as in landfill closures and miningapplications.

The heretofore used GSE UltraFlex® smooth geomembrane is a smooth linearlow density polyethylene (LLDPE) geomembrane according to thespecifications of Table 2 (which also meet GRI GM17).

TABLE 2 Minimum Average Value Tested Property Test Method Frequency 1.00mm 1.50 mm 2.00 mm 2.50 mm Thickness, mm ASTM D 5199 every roll 1.001.50 2.00 2.50 Lowest individual reading 0.90 1.35 1.8 2.25 Density,g/cm³, (max.) ASTM D 1505 90,000 kg 0.939 0.939 0.939 0.939 TensileProperties (each direction) ASTM D 6693, Type IV  9,000 kg 27 40 53 66Strength at Break, N/mm Dumbbell, 50 mm/min 800 800 800 800 Elongationat Break, % G.L. 50 mm Tear Resistance, N ASTM D 1004 20,000 kg 100 150200 250 Puncture Resistance, N ASTM D 4833 20,000 kg 250 370 500 620Carbon Black Content, % ASTM D 1603/4218  9,000 kg 2.0-3.0 2.0-3.02.0-3.0 2.0-3.0 (Range) Carbon Black Dispersion ASTM D 5596 20,000 kgNote⁽¹⁾ Note⁽¹⁾ Note⁽¹⁾ Note⁽¹⁾ Oxidative Induction Time, min A5TM D3895, 90,000 kg >100 >100 >100 >100 200° C.; O₂, 1 atm TYPICAL ROLLDIMENSIONS Roll Length, m Double-Sided Textured 265 171 131 103Single-Sided Textured Roll Width, m 6.86 6.86 6.86 6.86 Roll Area, m²Double-Sided Textured 1,819 1,171 899 710 Single-Sided TexturedNote⁽¹⁾ - Dispersion only applies to near spherical agglomerates. 9 of10 views shall be Category 1 or 2. No more than 1 view from Category 3.

The above described GSE UltraFlex® smooth geomembrane has been used inapplications that require increased flexibility and elongationproperties where differential or localized subgrade settlements mayoccur, such as in a landfill closures and mining applications.

As well as LLDPE such as described above, the sheet may alternatively beone or more of high density polyethylene (HDPE), polypropylene (PP),ethylene propylene diene monomer (EPDM), thermoplastic olefins (TPO),ethylene vinyl acetate (EVA) as well as LLDPE and/or other thermoplasticmaterials and their coextruded variations.

As one difference from sheets such as the above described GSE UltraFlex®textured or smooth geomembranes used in geotechnical applications, thegeosynthetic sheet according to the present invention is translucent ortransparent (and thus does not include carbon black).

Additionally, an ultraviolet light (UV) additive is included in thegeomembrane whereby UV protection may be provided by (and substantiallyonly by) a UV stabilizer. The UV additive may advantageously include ahindered amine light stabilizer (HALS) formulated to resistextraction/destruction by strong chemicals such as expected to beencountered in the temperature-driven process area to be covered by thesheet (e.g., such as concentrated sulfuric acid commonly utilized incopper mines to extract precious metals). HALS further introduces verylittle color or opacity to the geomembrane so as to not detrimentallyimpact the desired opacity of the sheet. Thermal stabilizers may also beadvantageously included to stabilize the geomembrane under elevatedtemperatures in addition to providing extended longevity due to asyngergistic effect between the UV stabilizer and the thermalstabilizer. The thermal stabilizers also resist extraction/destructionby chemicals and do not add color/opacity to the geomembrane.

Advantageously, the sheet may have a thickness of about 1.0 mm, althoughit should be understood that still other thicknesses might be used, withthe process area covered by a single layer of sheet. That is, as isknown in the geotechnical industry, sheets may be installed to coverlarge areas by laying out several rolls of material in the field side byside with about 6 inches of overlapping, with the overlap suitablybonded (as by heat welding) to form a closed seam.

Besides LLDPE, still other types of plastic materials mightalternatively or in combination be advantageously used to form thegeosynthetic sheet to improve the clarity of the geosynthetic sheet,such as high density polyethylene (HDPE), polypropylene (PP), ethylenepropylene diene monomer (EPDM), thermoplastic olefins (TPO), ethylenevinyl acetate (EVA) and/or other thermoplastic materials and theircoextruded variations. Further, it should be appreciated that variouslayer configurations within the sheet may be utilized, as well asclarifying agents and other additives, to provide a desired sheetclarity (translucence/transparency) and other properties such as UVstabilization, thermal stabilization, chemical resistance, mechanicalproperties, and others.

It should be appreciated that by utilizing such geosynthetic sheets tocover temperature sensitive geotechnical applications, heat loss fromthe underlying materials to the atmosphere can be reduced. Thus, moreheat may be retained in the underlying material or liquid, whichretained heat will increase the effectiveness of the process occurringtherein.

Further, the geosynthetic sheet will reduce the amount of evaporativeloss to the atmosphere. In applications that utilize a liquid,preventing the material loss of the liquid is important for maintainingthe composition of the liquid (e.g., in heap leach mining applications,retaining the liquid facilitates maintaining a proper chemicalconcentration in the leaching solution). Still further, in areas havingwet seasons and/or heavy rain events, the geosynthetic sheet willprevent water from being undesirably added to the process area, whichadded water could also cause undesirable dilution.

Still further, use of a geosynthetic sheet as disclosed herein allowsthe above advantages to be obtained without blocking inspection of thematerials, equipment and/or liquids below while the temperaturesensitive process takes place, and without exposure to the sun reducingthe desired useful life of the sheet.

1. A geotechnical application, comprising: a site having a process area,wherein said process area is temperature sensitive; a geosynthetic sheetcovering said site process area, said geosynthetic sheet including aultraviolet (UV) light stabilizer and thermal stabilizer and beingsubstantially impervious to water, and at least translucent to light. 2.The geotechnical application of claim 1, wherein said sheet is linearlow density polyethylene (LLDPE).
 3. The geotechnical application ofclaim 1, wherein said sheet one or more of linear low densitypolyethylene (LLDPE), high density polyethylene (HDPE), polypropylene(PP), ethylene propylene diene monomer (EPDM), thermoplastic olefins(TPO), ethylene vinyl acetate (EVA) and coextrusions thereof.
 4. Thegeotechnical application of claim 1, wherein said sheet reduces heatloss to air at the site.
 5. The geotechnical application of claim 1,wherein said sheet is sufficiently translucent to allow visualinspection of underlying materials in said process site through saidsheet.
 6. The geotechnical application of claim 5, wherein said sheet issubstantially transparent.
 7. The geotechnical application of claim 1,wherein said UV light stabilizer includes a hindered amine lightstabilizer (HALS) formulated to resist extraction/destruction bychemicals used in the geotechnical site process area.
 8. A geosyntheticsheet for covering a geotechnical site having a temperature sensitiveprocess area, said sheet including a ultraviolet (UV) light stabilizerand being substantially impervious to water, and at least translucent tolight.
 9. The geosynthetic sheet of claim 8, wherein said sheet islinear low density polyethylene (LLDPE).
 10. The geosynthetic sheet ofclaim 8, wherein said sheet one or more of linear low densitypolyethylene (LLDPE), high density polyethylene (HDPE), polypropylene(PP), ethylene propylene diene monomer (EPDM), thermoplastic olefins(TPC), ethylene vinyl acetate (EVA) and coextrusions thereof.
 11. Thegeosynthetic sheet of claim 8, wherein said sheet reduces heat loss toair at the site.
 12. The geosynthetic sheet of claim 8, wherein saidsheet is sufficiently translucent to allow visual inspection throughsaid sheet of underlying materials.
 13. The geosynthetic sheet of claim12, wherein said sheet is substantially transparent.
 14. Thegeosynthetic sheet of claim 8, wherein said UV light stabilizer includesa hindered amine light stabilizer (HALS) formulated to resistextraction/destruction by chemicals used in a covered geotechnical siteprocess area.
 15. The geosynthetic sheet of claim 8, wherein said sheetfurther includes a thermal stabilizer.